Task under Manage -> Tasks are only displayed in case the current user is part of the following system properties in Kie Server: org.jbpm.ht.admin.user (default: Administrator) or org.jbpm.ht.admin.group (default: Administrators).
By default, an empty list is returned when this criteria isn't met. Proposal is to fallback to the task association with Business Administrators, in case the current user or any of its groups have this relationship set in any tasks, these should be visible.